Re: [PATCH] modules fix incorrect percpu usage
From: Tejun Heo
Date: Tue Mar 30 2010 - 22:17:10 EST
On 03/31/2010 11:03 AM, Steven Rostedt wrote:
> I don't know. A possible "NULL pointer dereference" seems to me to be a
> pretty big user visible impact.
>
> I guess the question is, what's the risk of adding this change?
AFAICS, the risk is fairly low. per_cpu_ptr(pcpudest, cpu) is
SHIFT_PERCPU_PTR((ptr), per_cpu_offset((cpu))) which is just a fancy
way of saying "typeof(ptr)((unsigned long)(ptr) + per_cpu_offset(cpu))"
with enough obfuscation to prevent gcc from optimizing it incorrectly.
Thanks.
--
tejun
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